Lump on her head???

not sure i should be worried but tia has always had a lump between her ears to the back of her head where her skull finishes it's always been noticable and hard as if it were part of her skull but lately its got bigger about the size of a ping pong ball cut in half and placed under her skin on her head and is now a bit soft. she had her jabs 2weeks ago and the vet didnt seem concerned although i didnt mention it either. she's her usual energetic self and is often chasing my larger dog round the house like a looney and running into chairs doors etc, pretty much like any puppy i suppose. she's still eats her food although that has increased in the last few weeks but think that purely due to growth. drinks & toilets with no problems. she's as she was when i first got her but this lump looks stupid lol.

do you think i should be worried and take her to the vets or wait as it might just be a bump from banging her head?
She can play quite rough with my other dog who is size of a german shepherd and is often hanging of his collar ears tail or whatever she can get hold of lol he throws her around and she comes running for more they are absolutely mad!!!
Anyway any advice is much appreciated unfortunatley i cant seem to download any picks to show u

If it's always been there & it's now changing (ie going soft) I'd get it checked out by the vet. That's not to say it's anything nasty - it may just be a cyst that may or may not need draining. But you should probably find out.

If it has always been there, then I doubt it's anything to do with rough play.